The present invention provides a subscriber-implemented registration technique for use in a CDMA communication system to uniformly distribute subscriber load among base stations.
Typically in a CDMA system, when a subscriber terminal (“mobile station”) begins operation, it registers with a base station as part of its initialization operation. As part of registration, the mobile station typically identifies a pilot channel of a base station and communicates with the base station to identify the mobile station's presence in the base station's cell. The mobile station typically transmits a registration request message on an access channel associated with the base station or its pilot channel. When multiple pilot channels are detected, the mobile station typically registers with the base station whose pilot channel is associated with a highest quality reception.
As is known, CDMA communication systems are “interference limited.” Unless determined by a communication protocol, a base station is not characterized by a fixed number of communication channels by which it may communicate user data to mobile stations. In theory, a “congested” base station may continue to add communication channels to satisfy increased demand for service, but the communication quality of each channel in the system would be diminished incrementally. In practice, the number of channels that may be satisfied by a base station is determined by minimum call quality standards that are to be maintained by the communication system. As is known, this number of channels also may be affected by environmental conditions in the cell that may contribute to quality degradations. However, it is desirable to limit unnecessary communication in a congested CDMA cell to improve the call quality of communication channels already in process and to reduce undesirable cross-channel interference.
In traditional CDMA systems, a mobile station will attempt to register with a base station based solely on the mobile station's measurement of the received signal strength, Ec/Io or SNR of the pilot channels. Although provisions exist in some CDMA systems for base stations to refuse to register a mobile station based upon congestion levels of the base station, registration in such systems typically includes a first transmitted registration request message from the mobile station to the congested based station followed by a second transmitted message from the congested base station to the mobile station denying registration. The mobile station then would attempt to register with the base station associated with the next strongest pilot channel. And, in systems employing soft handoff, if the mobile station succeeds in registering with the next strongest base station, the mobile station may retry registration with the congested base station upon expiration of a countdown timer.
The registration request and denial transmissions that are used in these traditional CDMA systems consume precious bandwidth in an already-congested base station. They contribute to cross-channel interference with other channels already in progress and further consume processing resources in the already-congested base station. Accordingly, there is a need in the art for a low bandwidth registration protocol In a CDMA system, one that reduces processing demands upon a base station operating in a congested state.